The EPS system of the 3rd Generation Partnership Project (3GPP) mainly comprises an Evolved Universal Terrestrial Radio Access Network (E-UTRAN), a Mobility Management Entity (MME), a Serving Gateway (S-GW), a Packet Data Network Gateway (P-GW or PDN GW), a Home Subscriber Server (HSS), an Authentication, Authorization and Accounting (AAA) server of the 3GPP, a Policy and Charging Rules Function (PCRF) entity and other supporting nodes.
FIG. 1 is a schematic diagram of the system architecture of the EPS, and the MME is responsible for the control plane related operations such as the mobility management, signaling process of the non-access layer and management of the user mobility management context and so on; the S-GW is an access gateway device connected with the E-UTRAN, and forwards data between the E-UTRAN and P-GW, and is responsible for caching the paging waiting data; the P-GW is a border gateway of the EPS and the Packet Data Network (PDN), and is responsible for the PDN being accessed and for forwarding data between the EPS and the PDN and so on; the PCRF is a policy and charging rules function entity, which is connected with an operator Internet Protocol (IP) service network through a receiving interface Rx, and obtains service data, and besides, the PCRF is connected with gateway devices in the network through the Gx or Gxa or Gxc interface, and is responsible for initiating the IP bearer setup, ensuring the Quality of Service (QoS) of the service data, and carrying out the charging control.
The EPS supports the interworking with the non-3GPP system, and the interworking with the non-3GPP system is implemented through the S2a/b/c interfaces, and the P-GW is the anchor point between the 3GPP and the non-3GPP systems. In the architecture diagram of EPS system of FIG. 1, the non-3GPP system is divided into a trusted non-3GPP IP access network and an untrusted non-3GPP IP access network. The trusted non-3GPP IP access network can be connected with the P-GW through the S2a interface directly; and the untrusted non-3GPP IP access requires connecting with the P-GW through the Evolved Packet Data Gateway (E-PDG), and the interface between the E-PDG and the P-GW is the S2b, and the S2c provides the user plane related control and the mobility support between the User Equipment (UE) and the P-GW, and the supported mobility management protocol is the IPv6 Support for Dual Stack Hosts and Routers (DSMIPv6).
In the EPS system, the Policy and Charging Enforcement Function (PCEF) entity exists in the P-GW, and the PCRF and P-GW exchange information through the Gx interface. When the interface between the P-GW and the S-GW is based on the PMIPv6, the S-GW also has the Bearer Binding and Event Report Function (BBERF) entity to carry out the QoS control on the service data flow, and the S-GW and the PCRF exchange information through the Gxc interface. When accessed through the trusted non-3GPP access system, the BBERF also resides in the trusted non-3GPP access gateway. The trusted non-3GPP access gateway and the PCRF exchange information through the Gxa interface (the dotted line shown in FIG. 1). The Application Function (AF) which provides services to the UE sends service information used for making a Policy and Charging Control (PCC) policy to the PCRF through the Rx interface. In the 3GPP, the corresponding PDN network can be found through the Access Point Name (APN). Generally, a connection from the UE to the PDN network is called as an IP Connectivity Access Network (IP-CAN) session.
The EPS supports UE accessing one PDN network (namely the operator providing IP service located network) through multiple access networks at the same time, which is also called Multiple Access. As shown in FIG. 2, the UE is in the coverage of the non-3GPP access network and the 3GPP access network at the same time, and accesses the PDN network via the same P-GW through the non-3GPP IP access network and the 3GPP access network.
In this scenario, the P-GW allocates one IP address for UE, namely there is only one IP-CAN session between the UE and the PDN. The UE, P-GW or PCRF determines which access network connection the IP data flow is transmitted through according to different characteristics of the services. For example, the non-3GPP access network is the Wireless Fidelity (WiFi) network, and service data flows of the Hyper Text Transfer Protocol (HTTP) and File Transfer Protocol (Ftp) can pass through the connection of the WiFi access network, and at the same time service data flows of the Voice Over Internet Protocol (VoIP) based on the IP network can be sent to the user equipment through the 3GPP, and thus the services which have lower real time requirements such as the HTTP and Ftp and so on can take the advantage of lower tariff of WiFi; and the services which have higher real time requirements such as the VoIP and so on can take the advantages of the QoS control and the better mobility management of the 3GPP.
In the prior art, the AF is required to provide charging information of application layer to the Online Charging System (OCS)/Offline Charging System (OFCS) to be used for the charging of the application layer, and at this time, the AF is required to provide the IP-CAN type used by the current access service of user to the OCS/OFCS to carry out charging, and the IP-CAN type could also include the Radio Access Technology Type (RAT Type). However, in the prior art, one IP-CAN session of the UE can only have one IP Connectivity Access Network Type (IP-CAN Type) (further also includes one Radio Access Technology Type), and thus after the user establishes an IP-CAN session, as long as the PCRF reports the IP-CAN Type of this IP-CAN session or further carries the RAT Type, all the IP data flows of the service provided by the AF will be charged according to the IP-CAN Type or RAT Type. For the case of UE being accessed through the multiple access networks, how to make the application layer know this Multiple Access case and how to implement reasonable charging in the Multiple Access scenario, the prior art does not provide a solution. Similarly, the PCEF is also required to provide the charging information of the bearer layer to the OCS/OFCS to be used for the charging of the bearer layer, and for the case of UE being accessed through multiple access networks, how to implement reasonable charging in the Multiple Access scenario, the prior art does not provide a solution.